The western part of the forest is wetter than the dry and less temperate east. The vegetation varies similarly, from the western boreal forest, to the eastern high-elevation steppe. A 1993 Forest Service study estimated that the extent of old growth in the forest was 316,000 acres (128,000 ha),[4] a majority of which was lodgepole pine forests. Wildfires are not uncommon in the Okanogan National Forest. Notable fires include the 2006 Tripod Complex, the 2012 Okanogan Complex, and the 2014 Carlton Complex fires.

The Okanogan National Forest was established on July 1, 1911, from a portion of the Chelan National Forest. On July 1, 1921, the entire forest was transferred back to the Chelan National Forest, but on March 23, 1955, the transfer was reverted.[2]

The Conconully, Loomis, Squaw Creek, Sweat Creek, Twisp and Winthrop ranger districts were formed between 1911 and 1915.[6] On July 1, 1921, the entire forest reunited back into the Chelan National Forest, and the term Okanogan was discontinued.[9] Subsequently, another ranger district was established, the Chelan Ranger District. Portions of the Loomis Ranger District, along with the Sweat Creek Ranger District, absorbed to become the Loomis State Forest, later abandoned. The forest's ranger area underwent a number of smaller changes until the mid-1940s. The Squaw Creek Ranger District was absorbed by the Twisp Ranger District in the early 1930s, while the Forest Service Monument 83 lookout was constructed in neighboring British Columbia as an accident. The Pasayten Ranger District was later created from a portion of the Winthrop Ranger District, and the Conconully Ranger District became the Okanogan Ranger District.[6] The western part of the Colville National Forest transferred into the Chelan National Forest in 1943. On March 23, 1955, Chelan National Forest again became the Okanogan National Forest, then headquartered in the city of Okanogan. As per the change, the rename of the Conconully Ranger District was reverted.[9]

In 1968, the Pasayten Wilderness was established, introducing over 200,000 acres (81,000 ha) to the forest.[6] The United States Congress designated almost 65 percent of the forest's area as the Lake Chelan-Sawtooth Wilderness under the National Wilderness Preservation System around 1984, upon land formerly occupied by the former Chelan Division of the Washington Forest Reserve.[10] The Okanogan National Forest was administratively combined with the Wenatchee National Forest in 2000, although the boundaries for each forest remained unchanged, and in 2007, it administratively became known as the Okanogan–Wenatchee National Forest.[6]

360° panorama near the summit of Goat Peak in the Okanogan National Forest. Photographed on a September afternoon, this photo includes sweeping views of the Methow Valley and the greater Cascade Range including glaciated Silver Star Mountain. High ice clouds create sun dogs on either side of the sun. Goat Peak Lookout is prominent on the righthand side.